This invention relates to U.S. Pat. application Ser. No. 581,510 filed Feb. 17, 1984 and concerns a molten metal discharging device adapted to be mounted at a bottom portion of a container such as a ladle or tundish so as to control the discharge of the molten metal in the casting of molten metal or the like.
In the case of casting molten steel, for instance, by way of a conventional continuous casting process, a molten metal discharging device comprising a stationary plate and a slide plate is attached to the bottom portion or a ladle of tundish accommodating the molten steel and the flow rate of the molten steel is adjusted by causing the slide plate to move slidably with respect to the stationary plate thereby opening or closing a passage bore, in the stationary plate, for the molten steel. In the above-mentioned molten metal discharging device, an inert gas such as argon is introduced from the stationary plate into the molten steel so as to prevent the clogging in the passage bore caused by the solidification of the molten steels and/or deposition of oxides of metal or metalloid such as Al, Ti, Ca, Cr, Mn, Si or Ni.
The conventional molten metal discharging device of the type described above is shown in FIG. 1.
In FIG. 1, an upper nozzle 1 having a molten metal passage bore 1a is secured to a bottom portion of a tundish (not illustrated). Below the upper nozzle 1 is attached a molten metal discharging device 14 comprising an upper stationary plate 2, a slide plate 3 and a lower stationary plate 4 having molten metal passage bores 2a 3a, 4a respectively. The slide plate 3 moves slidably between the upper stationary plate 2 and the lower stationary plate 4 in the direction of A or B to open or close the passage bore 2a, 3a, 4a thereby adjusting the flow rate of the molten steel passing through the bores 2a, 3a, 4a and completely closing the bores 2a, 3a, 4a. The frame member 2b of the upper stationary plate 2 is made of dense refractory material and an annular, porous gas supply member 5 made of porous refractory material is tightly fitted over the entire circumference of the upper and enlarged inner circumferential wall surface 2c of the frame member 2b so as to define the passage bore 2a. A gas pressure-uniformalizing zone or uniform pressure zone 6 in the form of an annular space or chamber is defined between the annular porous member 5 and the frame member 2b of the upper stationary plate 2. Further, a gas introduction hole 7 communicated with the uniform pressure zone 6 is formed in the upper stationary plate 2, and a gas introduction pipe (not shown) is connected to the gas introduction hole 7. A submerged nozzle 8 is attached to the bottom of the lower stationary plate 4 and inserted at the lower part thereof into a mold 9. A metal member 15 constituting a part of the tundish is secured by means of cement mortar, for instance, to the upper stationary plate 2 of the molten metal discharging device 14.
In the illustrated device 14, molten steel poured from a tundish (not illustrated) is supplied through the passage bores 1a, 2a, 3a, 4a and 8a formed respectively in the upper nozzle 1, the upper stationary plate 2, the slide plate 3, the lower stationary plate 4 and the submerged nozzle 8 into the mold 9 and then cooled within and below the mold 8. As the result, a molten layer 10, a partially- or semi-molten layer 11 and a solidified layer 12 are formed within and after or below the mold 9. Mold powder layer 13 is provided above the molten layer 10.
In the molten metal discharging device 14 as described above, a gas is introduced from the gas introduction hole 7 into the molten steel through the gas supply member 5 to agitate the molten steel when the molten steel is started to be poured from the ladle to the tundish, thereby preventing the solidification of the molten steel within the passage bore 2a in the upper stationary plate 2 and facilitating the initial opening of the bore 2a. Further, the gas is introduced through the porous gas supply member 5 to agitate the molten steel also during casting for preventing the solidification of the molten steel and/or deposition of metal oxides to thereby prevent clogging in the bore 2a, etc. Furthermore, the supply of the gas serves the oxides or impurities in the molten steel to float up and to reduce the content of the oxides or impurities incorporated in the steels to 1/5-1/10 as compared with those steel products obtained without such gas supply.
However, the conventional molten metal discharging device 14 as described above has the following drawbacks:
Since only the gas introduction member 5 is made of porous refractory material and the frame member 2b is made of dense refractory material in the upper stationary plate 2, the stationary plate 2 has no sufficient heat-insulating property. As a result, there is fear that the metal member 15 covering the molten metal discharging device 14 may be distorted. Further, since the frame member 2b made of dense refractory material is a relatively good heat conductor through which the heat can be removed from the molten steel, clogging in the passage bore 2a caused by the solidification of molten steels or the like cannot be effectively avoided.